The present invention relates to a lithography technology, and more particularly, to a mask for an extreme ultra-violet (EUV) lithography and a method for exposure using the same.
A photo mask functions to form a desired pattern on a wafer while light is irradiated on a mask pattern formed on a substrate of a transparent material and transmitted light is transferred onto the wafer. As a pattern size of a semiconductor device is miniaturized with an increase in integration of the semiconductor device, there is shown a limitation in formation of a mask pattern. Particularly, as the semiconductor device is reduced to 30 nm technology or below, it is difficult to transfer a fine pattern onto the wafer with exposure equipment using an ArF wavelength. In one method for overcoming this limitation, a lithography process using an extreme ultra-violet ray (EUV) has been developed and used.
The EUV lithography process uses EUV light with a wavelength of 13.5 nm, which is shorter than that of KrF or ArF light used in a conventional exposure process. When using the EUV, the EUV is absorbed in most materials and is thus difficult to be used in a current method for exposure using transmission. Accordingly, a method for exposure by reflection of light, not a method for exposure using transmission of light has been studied. A mask used in the EUV lithography is formed including a mirror layer of a multi-layer structure of Mo/Si layers on a substrate. Accordingly, an absorber pattern is formed as a shape of a layout of a pattern to be transferred onto a wafer.
The lithography process using the mask for EUV lithography is expectedly able to exposure-transfer a pattern with a critical dimension of 32 nm onto a wafer at a depth of focus of about 150 nm. Nevertheless, a higher integration degree of a semiconductor device is required, and development of an EUV lithography process capable of obtaining higher resolution will be required if a critical dimension of a circuit pattern integrated on a wafer is reduced to 30 nm or less.
In an example of a method for obtaining a higher resolution in the EUV lithography process, there is a double patterning technology (DPT). The double patterning technology is a method of forming a pattern to be transferred onto a final wafer with a two step exposure processes using two masks. That is, a photolithography process for one layer is implemented using two divided masks, instead of using a single mask. In this case, a database is also divided into two masks. This double patterning technology has a problem that process steps become complex since two masks for a mask pattern, which is divided into two patterns, are fabricated and the exposure process is thus implemented two times. Also, if the mask is fabricated into two sheets, mask registrations occur respectively, resulting in a mask registration error. This mask registration error results in deterioration in overlay of exposure equipment upon the subsequent exposure process. Therefore, there is required a method which improves the mask registration error upon the EUV lithography process and thus can form a precise pattern on a wafer.